'require Carp;' has differnet meanings under 'use warnings;'?

demerphq has asked for the wisdom of the Perl Monks concerning the following question:

Im curious if anyone can explain why

 
require Carp;
Carp::croak "This will produce a compile time error.";
[download]

wont compile '(Do you need to predeclare Carp::croak?)' but

 
use Carp;
Carp::croak "This will compile fine.";
[download]

is fine and so is

 
use warnings;
require Carp;
Carp::croak "And so will this.";
[download]

I know that warnings does the use Carp; so the two are the same really, but why should it make a difference if Carp is used or required when the usage is via a fully qualified function call? I mean using a different module as the example works fine, so whats with Carp?

require Data::Dumper;
print Data::Dumper::Dumper([qw(This is good too)]);
[download]

Thanks in advance...

Yves / DeMerphq
--
When to use Prototypes?
Advanced Sorting - GRT - Guttman Rosler Transform

Comment on 'require Carp;' has differnet meanings under 'use warnings;'? Select or Download Code

Replies are listed 'Best First'.
Re: 'require Carp;' has differnet meanings under 'use warnings;'? by demerphq (Chancellor) on Mar 12, 2002 at 15:06 UTC
So thanks to arturo and tye I got to the bottom of this. The reason for the difference is that 'require' is a runtime directive whereas 'use' is a compile time directive. Now since I left off the parens on the croak the croak needs to be defined for perl not to get confused. So the way to solve this problem is either use the parens (best choice I would say) or to wrap the require statements in a BEGIN block. sigh So many subtleties, so little time... BTW: tye provided a little quote in the CB that I think is useful so Ill repeat tye: don't get confused into thinking that there is one "compile time" and one "run time". Each line (or less) of code can have different compile/run times Thanks all. Yves / DeMerphq -- When to use Prototypes? Advanced Sorting - GRT - Guttman Rosler Transform	[reply]
Re: Re: 'require Carp;' has differnet meanings under 'use warnings;'? by Juerd (Abbot) on Mar 13, 2002 at 15:46 UTC
So the way to solve this problem is either use the parens (best choice I would say) or to wrap the require statements in a BEGIN block. Is there a reason for not wanting to use Carp, instead of require it? If it's the importing, you could simply supply an empty list: `use Carp ();` [download] U28geW91IGNhbiBhbGwgcm90MTMgY W5kIHBhY2soKS4gQnV0IGRvIHlvdS ByZWNvZ25pc2UgQmFzZTY0IHdoZW4 geW91IHNlZSBpdD8gIC0tIEp1ZXJk	[reply] [d/l]
Re: 'require Carp;' has differnet meanings under 'use warnings;'? by VSarkiss (Monsignor) on Mar 12, 2002 at 15:44 UTC
Just to add fuel to the fire: your first example will work fine if you use parentheses, like so: `require Carp; Carp::croak("This works fine also");` [download] If Perl has compiled a `sub`, you can drop the parentheses when calling it. Otherwise you need to leave them in. But let's not get into prototypes....	[reply] [d/l] [select]